French soldiers stand guard as they prevent the access to the scene of an attack in Saint Etienne du Rouvray, Normandy, France, Tuesday, July 26, 2016. Two attackers invaded a church Tuesday during morning Mass near the Normandy city of Rouen, killing an 84-year-old priest by slitting his throat and taking hostages before being shot and killed by police, French officials said. (AP Photo/Francois Mori)

In this grab made from video, emergency services transport a person into a waiting ambulance in Normandy, France, Tuesday, July 26, 2016. Two attackers seized hostages in a church near the Normandy city of Rouen on Tuesday, killing one hostage by slitting their throat before being killed by police, a security official said. The identities of the attackers and motive for the attack are unclear, according to the official, who was not authorized to be publicly named. (BFM via AP)

French President Francois Hollande (C) flanked by Hubert Wulfranc mayor of Saint-Etienne-du-Rouvray (L) and French Interior Minister Bernard Cazeneuve (R), speaks to the press as he leaves the Saint-Etienne-du-Rouvray's city hall following a hostage-taking at a church of the town on July 26, 2016 that left the priest dead.
French President Francois Hollande that two men who attacked a church and slit the throat of a priest had "claimed to be from Daesh", using the Arabic name for the Islamic State group. Police said they killed two hostage-takers in the attack in the Normandy town of Saint-Etienne-du-Rouvray, 125 kilometres (77 miles) north of Paris.
/ AFP PHOTO / CHARLY TRIBALLEAUCHARLY TRIBALLEAU/AFP/Getty Images

A French police officer stands guard by Saint-Etienne-du-Rouvray's city hall following a hostage-taking at a church in Saint-Etienne-du-Rouvray, northern France, on July 26, 2016 that left the priest dead.
A priest was killed on July 26 when men armed with knives seized hostages at a church near the northern French city of Rouen, a police source said. Police said they killed two hostage-takers in the attack in the Normandy town of Saint-Etienne-du-Rouvray, 125 kilometres (77 miles) north of Paris.
/ AFP PHOTO / CHARLY TRIBALLEAUCHARLY TRIBALLEAU/AFP/Getty Images

French Minister of Foreign Affairs and International Development Jean-Marc Ayrault (C) holds a press conference in Tours on July 26, 2016 after the announcement of a priest killed by two armed assailants during an hostage-taking at a church in the Normandy town of Saint-Etienne-du-Rouvray, near the northern French city of Rouen. / AFP PHOTO / GUILLAUME SOUVANTGUILLAUME SOUVANT/AFP/Getty Images

French police officers and firemen arrive at the scene of a hostage-taking at a church in Saint-Etienne-du-Rouvray, northern France, on July 26, 2016 that left the priest dead.
A police source meanwhile confirmed that police killed two hostage-takers.
/ AFP PHOTO / CHARLY TRIBALLEAUCHARLY TRIBALLEAU/AFP/Getty Images

French police officers and firemen arrive at the scene of a hostage-taking at a church in Saint-Etienne-du-Rouvray, northern France, on July 26, 2016 that left the priest dead.
A police source meanwhile confirmed that police killed two hostage-takers.
/ AFP PHOTO / CHARLY TRIBALLEAUCHARLY TRIBALLEAU/AFP/Getty Images

French police vehicles and firemen arrive at the scene of a hostage-taking at a church in Saint-Etienne-du-Rouvray, northern France, on July 26, 2016 that left the priest dead.
/ AFP PHOTO / CHARLY TRIBALLEAUCHARLY TRIBALLEAU/AFP/Getty Images

One of the terrorists involved in slitting the throat of a priest in Normandy was wearing an electronic surveillance tag at the time of the attack.

France's anti-terrorism prosecutor said the man, identified as 19-year-old Adel Kermiche, also evaded police twice using relatives' identities in attempts to reach Syria.

Francois Molins, Paris prosecutor, said Kermiche's tag was deactivated for a few hours every morning, corresponding with the time of the attack.

Speaking at a press conference, he explained the attacker - who was shot dead by police - was arrested in Germany in March 2015 trying to join extremists in Syria using his brother's identity, and then was arrested in Turkey two months later using a cousin's ID.

Kermiche, was a local teenager whose parents flagged his radical behaviour to authorities and grew up in a housing project in Saint-Etienne-du-Rouvray, the town where father Jacques Hamel was slain.

The second assailant has not yet been identified.

French authorities said the men had fake explosives and used nuns within the church as humans shields as police tried to enter the place of worship.

One had three knives and a fake explosives belt, while the other carried a kitchen timer wrapped in aluminum foil and had fake explosives in his backpack.

Mr Molins said the attackers, who claimed allegiance to Islamic State, also cried "Allahu Akbar" during the attack on 86-year-old Father Jacques Hamel.

He added that a minor, believed to be a 16-year-old younger brother of somebody wanted by police for trying to go to Syria or Iraq in 2015, has been detained in connection with the investigation.

Police raids are still under way.

A nun, identified as Sister Danielle, described how Father Hamel was forced to kneel on the floor before his throat was slit during the hour-long hostage-taking incident which began as the two knifemen burst into the parish church by a back door during morning mass.

She said: "They forced him to his knees. He wanted to defend himself. And that's when the tragedy happened.

"They recorded themselves. They did a sort of sermon around the altar, in Arabic. It's a horror," she told BFM television.

Sister Danielle went on to describe the minister as a "great priest".

One elderly parishioner was also wounded in the attack, but was no longer in a life-threatening condition on Tuesday night.

French president Francois Hollande pledged to fight the Islamic State terror group "using all means possible".

Addressing France on Tuesday, he said: "To attack a church, kill a priest, is to profane the republic."

Adding that the country was "waging war", he urged his compatriots to stay united and not turn against each other.

Mr Hollande said: "What terrorists want is to divide us, separate us, set us against each other", vowing: "We will win this war."

The attack in Normandy sent shock waves through a nation already reeling from the murder of 84 people in Nice on July 14, when a Tunisian national drove a lorry into crowds enjoying Bastille Day fireworks, as well as earlier atrocities directed at rock fans and sports crowds and the Charlie Hebdo magazine in Paris.

At a press conference in Downing Street, Prime Minister Theresa May offered her condolences to the French people, saying: "Our thoughts and prayers are with all those affected.

"We all face a terror threat. If you look at the national threat level here in the United Kingdom, it is at severe. That means that a terrorist attack is highly likely.

"What is necessary is for us all to work together, and stand shoulder to shoulder with France. We offer them every support we have in dealing with this issue and this threat that they, and the rest of us, are facing.

"But on one thing, I think, we are all absolutely clear, and that is the terrorists will not prevail.

"They are trying to destroy our way of life. They are trying to destroy our values. We have shared values and those values will win through and the terrorists will not win."

Despite there being no specific intelligence relating to attacks against the Christian community in the UK, the National Police Chiefs' Council is urging the community to be alert but not alarmed, report concerns and review their security as a precaution.

National Operational Police Lead for Protect and Prepare, Deputy Assistant Commissioner Neil Basu said: "There is no specific intelligence relating to attacks against the Christian community in the UK. However, as we have seen, Daesh and other terrorist groups have targeted Christian as well as Jewish and other faith groups in the West and beyond.

"Following recent events in France, we are reiterating our protective security advice to Christian places of worship and have circulated specific advice today. We are also taking this opportunity to remind them to review their security arrangements as a precaution."

Following the attack, religious leaders, including those from the Muslim community, issued messages of sympathy and solidarity in the wake of the killing.

In a statement, the Vatican said Pope Francis shared the "sorrow and horror" felt over the incident, adding: "We are particularly struck because this horrible violence has occurred in a church - a sacred place where we pronounce God's love - with the barbaric murder of a priest and worshippers affected."

Archbishop of Canterbury Justin Welby said: "Evil attacks the weakest, denies truth and love, is defeated through Jesus Christ. Pray for France, for victims, for their communities."